1. Field of the Invention
The present invention relates to a power tool, such as a hammer and a hammer drill, which is capable of regulating internal pressure of an accommodating space for a driving mechanism.
2. Description of the Related Art
Japanese non-examined laid-open Patent Publication No. 2004-508949 discloses an electric hammer drill capable of regulating the internal pressure of a gear housing. A driving mechanism to drive a tool bit is housed in the gear housing and is driven by a motor. The gear housing is filled with grease for lubricating the driving mechanism and is hermetically sealed so as to prevent leakage of the lubricant to the outside. In the known art, a spiral groove is formed in the outer surface of the rotating shaft mounted to the gear housing to function as a pressure regulating passage via which an inside and an outside of the gear housing communicate with each other. Further, a rotating member is provided on the rotating shaft. The rotating member allows the spiral groove to communicate with the inside of the gear housing when the rotating member rotates together with the rotating shaft, while it interrupts such communication when the rotating shaft is stopped. In this manner, the internal pressure is regulated so as not to excessively increase when the rotating shaft is rotated. As a result, a leakage of lubricant from the gear housing can be alleviated.